The 4-sided surface has been substituted by the NURBS surface (see NURBS surface). This new entity has all the functionality of the old one.
Note: It is still possible, however, to access to this function with the Right buttons menu (see Tools).
Inside this option, GiD creates as many 4-sided surfaces as it can find. Every new surface will be created in the current layer.
Caution: When creating more than one surface at a time, some undesired surfaces may also be created. It is necessary to check the surfaces after creation and erase the undesired ones.